What was done
The authors quantified the temporal evolution of the productivity and "staying power" of fourteen species of plants across an experimental grassland diversity gradient that was established in the spring of 1994 at the Cedar Creek Natural History Area in central Minnesota, USA.

What was learned
Over the course of the long-term study, certain species were found to be overyielders, i.e., plants that grow better and produce more biomass when grown in competition with other species than when grown by themselves in monoculture. In this study there were six such species, including a C3 grass, three C4 grasses and two legumes; and Lambers et al. note that these "overyielding species were either superior N competitors (C4 grasses) or N fixers (legumes)." On the other hand, underyielding species, of which there were five in this experiment (four of which were forbs), typically grow less robustly when in the presence of other species. Nevertheless, the researchers determined that "overyielding species are not [our italics] displacing underyielding species over time."

What it means
Among other things, Lambers et al. conclude that "diversity-promoting interactions also operate in this experiment," and that "underyielding species appear to be buffered from extinction."

How common is this phenomenon? No one knows; but its operation in this study suggests that earth's plants may be much better "buffered from extinction" than many have supposed. More research ought thus be directed to better elucidating the "diversity-promoting interactions" that maintain the existence of underyielding species in the face of what might logically be presumed to be significant competitive pressure from average and overyielding species. In addition, consideration should be given to how the phenomena responsible for enabling underyielding species to avoid extinction may be influenced by global warming and rising atmospheric CO2 concentrations.